Add support for separate Credit/Debit columns

[nielsmaerten]

Feature request

Description

Also pointed out by u/Zendio on Reddit:

Some banks put Inflow and Outflow in the same column and represent both as positive numbers.
Whether a transaction is going in or out of the account, is indicated by a separate column.

ynab-buddy is currently unable to work with this format, but several banks (in Sweden, Finland and The Netherlands) use it. (source: bank2ynab's csv definitions)

Motivational note...

If I want to keep up the claim this tool works with any bank, this should be implemented ;)